After reading the recent post on the always fatal prion disease known as "chronic wasting disease" spreading in wild deer and elk in the U.S., a reader asked whether chronic wasting disease (CWD) is also found in cattle. Or whether it could cross over to cattle, and so wind up in the beef we eat. Excellent question.
The studies and medical discussions that I read all agreed that: chronic wasting disease is only found in cervids - deer, elk, reindeer, and moose. Medical opinion is that there is a species barrier, a "thin molecular barrier" preventing crossing over of the prion disease to cattle and humans. Several studies that specifically looked at this issue back this up. Whew, what a relief!
A 2017 study by Canadian researchers reviewed 23 studies looking at "transmissibility" of CWD to humans. They did not find any evidence of transmission of CWD prions to humans in the U.S or Canada, and no evidence supporting the possibility of transmission of CWD prions to humans. However, they did not rule out the possibility that a CWD prion more readily transmissible to humans could emerge over time given sufficiently extensive human exposure, or if a variation in CWD prion strains develops.
A good study by Univ. of Wyoming researchers actually had deer sick with CWD and healthy cattle living side by side for 10 years - sharing food, water, paddocks, and with constant interaction. Another group of 12 calves were given orally (by mouth) 45 g of prion tissue from CWD infected deer and kept indoors (2 per room) in an isolation building after that point. (Note that eating only 1 g of such prion tissue makes deer sick with CWD). There was also a healthy control group not exposed to CWD in any way. All brains were examined after death - and all cattle brains were normal.
Interestingly, this 2018 study did mention that if CWD prion material is injected into cattle brains (which was done in some other studies), then they do go on to develop CWD - but that is not how cattle would be exposed to it naturally. Which is why they did the study trying to mimic natural conditions in which any potential transmission could occur - and found no transmission of CWD.
But...scientists are concerned with possible transmission of CWD prions to humans occurring at some point, for example if variation in CWD prion strains develops. Keep in mind that CWD is spreading year by year throughout the US (which should be of special concern to hunters). There are many, many questions at this point.
Excerpts from Elizabeth S. Williams et al. (2018) in the Journal of Wildlife Diseases: CATTLE (BOS TAURUS) RESIST CHRONIC WASTING DISEASE FOLLOWING ORAL INOCULATION CHALLENGE OR TEN YEARS' NATURAL EXPOSURE IN CONTAMINATED ENVIRONMENTS
Abstract: We conducted a 10-yr study to establish whether chronic wasting disease (CWD) was readily transmissible to domestic cattle (Bos taurus) following oral inoculation or by cohousing cattle with captive cervids in outdoor research facilities where CWD was enzootic. ...continue reading "Chronic Wasting Disease Does Not Spread to Cattle and Humans"